In the use of plastic bags and packages, particularly for foodstuffs, it is important that the bag be hermetically sealed until the purchaser acquires the bag and its contents, takes them home, and opens the bag or package for the first time. It is then commercially attractive and useful for the consumer that the bag or package be reclosable so that its contents may be protected. Flexible plastic zippers have proven to be excellent for reclosable bags, because they may be manufactured with high-speed equipment and are reliable for repeated reuse.
A typical zipper is one which has a groove at one side of the bag mouth and a rib at the other side, which rib may interlock into the groove when the sides of the mouth of the bag are pressed together. Alternatively, a member having a plurality of ribs may be on one side of the bag mouth, while a member having a plurality of channels may be on the other side, the ribs locking into the channels when the sides of the mouth of the bag are pressed together. In such a case, there may be no difference in appearance between the two members, as the ribs may simply be the intervals between channels on a strip which may lock into another of the same kind. In general, and in short, some form of male/female interengagement is used to join the two sides of the bag mouth together. The so-called members, or strips, are bonded in some manner to the material from which the bags themselves are manufactured. Usually, pull flanges extend above the rib and groove strips, which pull flanges may be pulled apart for access to the interior of the bag.
Although flexible zippers of this variety are quite popular, they do not always prevent the inadvertent or unwelcome opening of a bag or package within the store, and various additions have been made to provide tamper-evident seals which would reveal when it has been opened prior to purchase. The problem of providing a tamper-evident zipper is exacerbated in package designs wherein the zipper is provided with a slider. While a slider facilitates a consumer opening and reclosing the package and hence is desirable in some instances, the slider makes it difficult for the manufacturer to employ conventional techniques to render the package tamper evident.
It is known to provide a zipper package construction which is designed to undergo some permanent change in the package appearance when the package is opened for the first time. In particular, it is known to provide a zipper package with a sealed header which extends over the zipper and encloses the zipper and slider. For example, the header may comprise extensions of the front and rear package walls, the extensions being joined by a seal. The seal may be a peel seal, which may be readily ruptured by a consumer to expose the zipper and slider, or a “hard” seal, the latter being a seal that is not intended to be broken. In the case of a header formed using a hard seal, it is known to provide the package header with one or more lines of perforations which must be torn open by a consumer to obtain access to the slider. In place of a line of perforations (or to facilitate tearing the package along the line of perforations), it is also known to provide one or more notches at a side edge of the header for starting a tear across the header. In any event, the header must be opened before access can be had to the slider and zipper. If a package evidences a torn header before the package is purchased by a consumer, this should indicate to the consumer that the package has been tampered with, e.g., previously opened.
Zipper package constructions with sealed headers should also have other desirable features. For example, the package should be “user friendly” in the sense that the steps necessary for the initial opening of the package prior to the use of the zipper are obvious or intuitive to the consumer. Also the zipper package design should allow the package to be formed on conventional packaging equipment with little or no modification of the equipment being required.